Today, in a lot of areas of high technology (integrated optics, μ-electronics, nanotechnology, aeronautics, (outer)space, automotive etc.) there are significant demands on new (polymeric) materials with outstanding and new properties. In order to satisfy such demands, a variety of high-performance polymers have been developed. Under these are polycyanurate ester resins and perfluorocyclobutyl (PFCB) polymers.
Polycyanurate ester resins are a lesser known class of high-performance-polymers, developed in the late 1960s as a base material for printed circuit boards. They show a number of outstanding properties, for example high thermal stability (Tg typically around 250-400° C.), low optical loss, low birefringence, low dielectric constant, good adhesion properties on different substrates, excellent resistance against most common solvents and amazing mechanical properties. They are used as encapsulants and adhesives, as underfiller in microelectronics, as low-k materials, in flame stable composites, in laminates, as friction materials, in lightweight construction, in automotive engineering, in the aircraft industry, and for outer space applications. The resins are prepared from cyanate monomersN≡C—O—R—O—C≡Nwhere residue R can be e.g. a fluorinated or semifluorinated (partly fluorinated) aliphatic chain, a residue comprising or consisting of one or more than one aromatic rings, the ring(s) directly linked to each other through a C—C bond or linked to each other via —O—, —S—, —CR17R18—, —SO2—, wherein R17, R18 are an optionally substituted alkyl group or aryl group. Alternatively, R can also be selected from the group comprising napthalene, anthracene or higher homologues. Residue R can also contain additional (third, fourth etc.) cyanato-groups.
The monomers are typically obtained by reacting respective, —OH containing compounds with halogencyanide under alkaline (basic) conditions as reported by Bauer and Martin (MARTIN, D.; BAUER, M.: cyanic Acid Esters from Phenols: Phenyl cyanate. In: Organic Synthesis 61 (1981), pp. 35-38). The said monomers undergo polycyclotrimerization to generate polycyanurates as shown below. In this trimerization reaction, an (at least) difunctional cyanate molecule will react with two other cyanate molecules to form a triazine ring. In case of using difunctional cyanates, i.e. compounds carrying two OCN groups, this triazine will comprise three free reactive —OCN groups and, under respective conditions, will react with further monomers to form pentamer, heptamer or higher oligomers, until a highly branched three dimensional network is built up. At sufficiently high temperatures and appropriate reaction times an almost complete transformation of the cyanato-groups can be achieved. No byproducts are found for this reaction. (see scheme (I) below):

Such polycyanurates show a number of outstanding properties, like high thermal stability, low optical loss, low dielectric constant, good adhesion properties on different surfaces and high mechanical strength. This makes these reactive resins suitable for a lot of applications.
Perfluorocyclobutane-polymers can be obtained from at least difunctional TFVE-containing-monomers:

Via thermal cyclodimerization. The exothermic formation of the cyclobutyl linkages does not require catalysts or initiators nor does the polymerization produce condensates or by-products.
Two trifluoroviylidene-groups are able to react (thermally initiated) with each other under formation of a PFCB ring. Based on difunctional monomers, (thermoplastic) linear polymers are formed:

In the above PFCB monomers and polymers, R1 and R2 can be chosen from residues comprising or consisting of one, two or even more aromatic rings, the rings directly linked to each other or linked via —C—, —O—, —S—, —SO2—, —CR17R18—, where R17, R18 are independently selected from optionally substituted alkyl groups or aryl groups. The aromatic ring(s) may contain one or more additional residues comprising other (functional) groups (e.g. —F, —Cl, —Br, —COOH, NH2, NO2 etc.).
Using at least trisfunctional monomers, the cycloaddition of the trifluorovinylidene-groups will yield a three-dimensional dense and crosslinked thermosetting polymer:
where R2 is defined as in the formulae above.
Initially developed at The DOW chemical company, the general class of PFCB polymers was originally targeted for microelectronics applications.
By this unique fluoropolymer technology, based on perfluorocyclobutyl (PFCB) aromatic ether repeating units, materials are provided which exhibit thermo-mechanical robustness (e.g., Tg>200° C.) and solution processability. Perfluorocyclobutyl (PFCB) polymers and copolymers have demonstrated a superior combination of optical and structural properties including: low transmission loss, especially at the important telecommunication wavelengths around 1500 nm, unprecedented melt and solution or solventless processability, and tailorable refractive index and thermoptic coefficients. First generation PFCB optical polymer technology has been commercialized by Tetramer Technologies, L.L.C, Clemson, SC, USA.
The PFCB polymers show a number of outstanding properties, like high thermal stability, low optical loss, low dielectric constant, high transparency and good fracture stability, good fracture toughness and hardness.
However, depending on a particular application as desired, none of the said polymer classes is able to meet all requirements at the same time.